A wide range of sunglasses are available, including prescription sunglasses, polarized sunglasses, and multifocal sunglasses (such as those with bifocal segments).
Prescription lenses are generally made by grinding relatively thick lens blanks down to the shape needed for the prescriptions. Such lens blanks are often about 9 millimeters thick before grinding. Of course, because of this thickness, the lens cost is higher than that for thinner lens blanks.
Besides prescription uses, thick lens blanks have been used with polarizing films to create polarized lenses, they have been tinted for filtering, they have been made with bifocal segments for multifocal applications, and they have been used in applications that combine each of these. In each of these applications, significant costs and processing time are involved in grinding the lens blanks so that their thickness is suitable for wearing.
Thinner lens blanks, often referred to as “plano” lenses, are less expensive, and have a thickness of about less than 5 millimeters. Such plano lenses have been used with polarizing films to create polarized lenses, they have been tinted for filtering, and they have been made with bifocal segments for multifocal applications. However, to the inventor's knowledge, no plano lenses have been made with a multifocal segment (such as a bifocal) and polarization. Thus, a need has arisen for polarized sunglasses and lenses that include multifocal segments and which are made from thin lens blanks.